1. Field of the Invention
The present invention relates to a portable terminal apparatus capable of performing data input and having a liquid crystal display (LCD) for displaying characters and the like and, more particularly, to a portable terminal apparatus having a pressure-sensitive tablet (to be referred to as a touch panel hereinafter) as a handwritten data input means.
2. Description of the Prior Art
In a conventional portable terminal apparatus which has a display constituted by an LCD to display characters and the like and which is capable of performing handwritten data input, a transparent touch panel is adhered and fixed to the LCD. When handwritten data is input on the touch panel, it is input to the terminal apparatus. In a terminal apparatus of this type, a software keyboard is displayed on the LCD region where the touch panel is arranged. The user points a portion of the touch panel corresponding to a key displayed on the keyboard, thereby inputting target sentences. Since the LCD also need to display the contents of the input sentences, the entire surface of the LCD must be partitioned into the keyboard region and the display region, inevitably reducing the respective areas. As a result, when a large number of keys are displayed on the keyboard region, the individual key size becomes small. Then, the pointing operation described above becomes difficult to perform, and an erroneous operation such as operating an adjacent key tends to occur easily. When the area of the keyboard region is increased, the area of the display region is decreased. Then, the sentences that can be displayed become short, making it difficult to recognize and edit the sentences.
In this manner, the technique described in the official gazettes is effective in that it enables accurate key input even when the software keyboard is displayed small. However, to display a software keyboard in a small size is limited, the conventional technique cannot drastically solve the problems described above, and the problem of the limited display region area still remains.
In addition to the problem of the display area, since the touch panel is adhered to the surface of the LCD, when the touch panel is damaged, the touch panel must be replaced together with the LCD. This makes the repair cumbersome and increases the repair cost imposed on the user. Since the LCD display contents are observed through the touch panel, the readability of the display is worse than in a terminal apparatus having no touch panel. Usually, a touch panel has a light transmittance of about 80%. In particular, the readability of an LCD having no backlight is considerably degraded.
In order to solve these problems, in Japanese Unexamined Patent Publication No. 8-221169, a software keyboard display method is proposed in which after a key which is pointed first is recognized by the terminal apparatus, a key which will be pointed next is estimated, and the estimated key is displayed larger than other keys. Even when a large number of keys are displayed, a key which is highly likely to be pointed next is displayed larger than other keys. This is effective in preventing an erroneous operation as described above caused by the small key size. Japanese Unexamined Patent Publication No. 8-234909 proposes a technique with which, upon pointing a key, if an adjacent key is also erroneously pointed simultaneously because of the small key size, only the corresponding region is displayed large and re-pointing is allowed to enable accurate key input.